Two features of the new materials which may result from the chemical modification of these 2:1 clay minerals are an enhanced capacity to exchange cations from solution (i.e. a cation exchange capacity) and/or an increase in the available surface area when compared with the properties of the initial starting mineral. These two features are of considerable significance to the cost-effective use of these derivative materials in a wide range of applications for cation-exchange (e.g. for removal of toxic metal ions from aqueous and non-aqueous solutions; removal of NH.sub.4.sup.+ from aqueous and non-aqueous solutions, as detergent builders and as water softeners), absorption (e.g. for the removal of gases from the environment, for absorption of cations from solutions), as agents for the controlled release of desired cations into an environment and as substrates for catalysis reactions in the modification of hydrocarbons and other chemicals.
Clay minerals are part of the larger family of minerals called phyllosilicates--or "layer" silicates. These clay minerals are typically characterised by two-dimensional arrangements of tetrahedral and octahedral sheets, each with specific elemental compositions and crystallographic relationships which define the mineral group. Thus, the tetrahedral sheet may have the composition T.sub.2 O.sub.5 (where T, the tetrahedral cation, is Si, Al and/or Fe) and the octahedral sheet may commonly contain cations such as Mg, Al and Fe, but may also contain other elements such as Li, Ti, V, Cr, Mn, Co, Ni, Cu and Zn (Brindley and Brown, Crystal Structures of Clay Minerals and their x-ray identification, Editors G. W. Brindley and G. Brown, Mineralogical Society, London, 1980). Each of these clay mineral groups can be further classified into trioctahedral and dioctahedral varieties, depending on the occupancy of the octahedra in the respective sheet arrangement(s). Some specific mineral species may show cation occupancies which are intermediate between the two varieties. Nevertheless, the relative arrangement of these tetrahedral and octahedral sheets also defines the basic mineral groups in that an assemblage which links one tetrahedral sheet with an octahedral sheet is known as a 1:1 type mineral. An assemblage which links two tetrahedral sheets with one octahedral sheet is known as a 2:1 mineral. This basic classification of mineral species, based upon the crystallographic relationships of specific sub-units, is well-known to those skilled in the art of clay mineralogy and forms a basis for description of this invention.
The production of an amorphous derivative, termed "kaolin amorphous derivative" (KAD), from kaolin clays which are 1:1 alumino-silicates, has been described in an earlier disclosure (WO95/00441). We have now surprisingly found that an amorphous derivative can also be manufactured from 2:1 clays which include montmorillonites and other members of the smectite group. The production of an amorphous derivative from these 2:1 clays is surprising insofar as the structure and chemistry of these minerals is markedly different to that of the 1:1 kaolin group minerals. A unit layer of the clays in the kaolin group consists of one octahedral sheet and one tetrahedral sheet so that both sheets are exposed to the interlayer space, a region which is accessible to reacting species. However, a 2:1 clay mineral comprises one octahedral sheet and two tetrahedral sheets. The octahedral sheet, which contains octahedrally coordinated aluminium, is sandwiched between the tetrahedral sheets. The transformation of this octahedral sheet is not readily predictable using metal halides since the interlayer space is surrounded by tetrahedral sheets. It is also relevant to point out that the octahedral sheet in 2:1 clay minerals would not be readily accessible to metal halides. It would be assumed by those skilled in the art that reacting species with 2:1 clay minerals would provide different products to reaction products described in WO95/00441 for these reasons.